Bleaching chemical pulp



Patented Feb. lib, 193? A acuity rice arr-uses BLEACHMG ornament. roar Wilhelm lhirschlsind, Berkeley, can, assignor to Great Western lElectro-Chemical Company, a corporation of (California N Drawing. Application September 211, i036,

Serial No. 101392 Claims.

This invention relates to the treatment of chemical wood pulps, particularly kraft, sulphite and soda pulps. I have found that chemical wood pulps can be effectively lightened in color by the addition of hydrosulphites in organic combination. The principal representatives of these compounds are given in the following:

Sodium hydrosulphite formaldehyde NazSzOaZCHzO Zinc hydrosulphite formaldehyde ZnS2O42CH2O Chemical pulps, when ready for the bleaching operation usually have a pH very close to that of an alkaline condition, sulphite pulp normally running about 6.5 and lower, and kraft and soda pulp between 6.8 and 7.5. I have found that a satisfactory bleaching operation can be secured if the pi-I of the pulp is adjusted in any suitable manner, as by addition of a suitable alkali, alkaline salt, acid or an acid salt, so that the pH is in the neighborhood of 5, and preferably between 4 and '7. The pH of the pulp is usually out of the range specified and beyond 5. If it is too acid I add an alkali or an alkaline salt as borax, soda ash and lime. If it is too alkaline I use a suitable acid or acid salt and I have effectively utilized sodium acid sulphite, sodium acid phosphate, sodiiun bisulphite, sulphur dioxide, sulphite cooking liquor, and as the acid sulphuric acid. Calcium salts can be used with sulphite but not with lrrait pulp. A

As suitable compounds which I can use I mention any aldehyde or ketone additionfproduct of hydrosulphurous acid.- In the formulas heretorore set forth the aldehyde can be any other aldehyde, such as acetaldehyde, or the aldehyde can be substituted by a ketone, such as acetone or any other hetone, while the metal can be replaced by forming the a rectiy therein by methods well mown ror the by zinc, potassium, magnesium or by the ammonium radical. The outstanding characteristics of the compound useful in accordance with this invention are that they are quite stable at ordi nary temperatures, and that their bleaching effeet is exerted between about 100 deg. F. and 212 deg. F. V

In utilizing the process of my invention I either add the compound as a solid, in the form of a solution, to the material to be bleached, or else 1 form the compound in situ in the material un- .dergoing bleaching. Thus I have bleached ulp by adding to the hot pulp at about 180 deg. F. zinc hydrosulphite formaldehyde in a small amount, usually between 0.25% and 3%. The pulp reduced quickly a considerably lighter and. more permanent color than one bleached with the usual reducing bleaches. i have also successfully bleached pulp hydrosulphite formaldehyde di in color and finished with l manufacture of this material. For instance, zinc hydrosulphite formaldehyde can be produced directly from zinc hydrosulphite and formaldehyde, 2

or from zinc dust, formaldehyde and a sulphite.

in oneprocess conducted according to my inventionfl added to 100 pounds (air dry basis) of sulphite pulp sufiicient water to make the pulp up to a 5% density. The pulp suspension was at 140 deg. F. and slightly below the preferred pI-I of 5. i added 0.3 pound of borax to the suspension and then a pound of zinc hydrosulphite and half a pound of a 30% formaldehyde solution. in ten to fifteen minutes the pulp brightened inaterially, and in less than thirty minutes the maximum brightening was attained. The bleach is then drained ofi and the pulp made into paper. Both Isetones and aldehydes form addition products with a hydrosulphite so that any aldehyde or ketone can be used. mula for an aldehyde and a ketone is where R is hydrogen for an aldehyde and any organic radical for a hetone wherein a carbon is bonded to the carbon in the formula. Any aldehydic or ketonic compound, aliphatic or cyclic, including carbocylic as well as heterocyclic, within these formulas can be used.

I. claim: 7

l. The process of bleaching a chemical pulp comprising subjecting said pulp to the action of an aldehyde and a hydrosulphite at a pH substantially between and '7, and at a temperature between 100 deg. F. and 212 deg. F. 2. The process of bleaching a chemical pulp comprising subjecting said pulp to the action of a ketone and a hydrosulphite at a pH substantlally between i and 7 at a temperature between 100 deg. and 212 deg;

3. Bleaching a chemical ,pulp at a temperature between 100 deg. and 212 deg. and a pH be,-

tween 4 and I! with an addition product of hydrosulphurous acid and an organic compound of the :tormula where R is any organic radical and R is hydrogen or any organic radical.

The simplest for- I where R is an allwl or aryl group and R is hydro- I 

